1. Field of the Invention
This invention relates to an electrical shock-preventable key unit which can prevent the occurrence of an electrical shock in a human body due to the discharge of static electricity upon locking or unlocking a door with a key.
2. Description of the Piror Art
In the case where a man stays in a building such as an office, a hotel, etc. with a carpet on its floor, his body is apt to be charged with static electricity. Thus, when he inserts a key with his hand in the lock of a door for locking or unlocking same, the static electricity charged on his body discharges instantaneously through the key to the earthed door. As a result, he oftens get a shock of electricity. On the other hand, as for a motorcar, since the car body is insulated from the earth by rubber tires and is not electrically connected to the ground, the car body is charged with static electricity. Thus, when a driver inserts a key into a door lock of the car, the static electricity charged on the car body sometimes discharges to his body through the key, thereby giving him in electrical shock.
In order to solve these problems, the present inventor has proposed a key unit which can prevent an electrical shock upon locking or unlocking with a key in Japanese Utility Model Laid-Open No. 91962/1986. FIGS. 1(a)-1(c) depict the proposed key unit. FIG. 1(a) is a plan view of the key unit, FIG. 1(b) is a plan view of the key unit, with the upper half of a case removed, and FIG. 1(c) is a view for illustrating an adapter. In these Figures, the reference numeral 1 represents the key unit which comprises a key body 2, a case 3, conducting plates 4 (4a, 4b), an adapter 5, a contact piece 6 and a resistor 7. The key body 2 is made of a conductive material and comprises a key portion 2a and a grip portion 2b. The key portion 2a projects from the case and is adapted to be inserted into the key hole of a door to be unlocked or locked. The case 3 comprises an upper half 3a and a lower half 3b each of which is made of an insulating material and which define an accommodating chamber for accommodating the key body 2. The upper half 3a is of the same construction as the lower half 3b and is fixed to the lower half 3b. The conductive plates 4a and 4b are provided on the surfaces of the upper half 3a and the lower half 3b, respectively. One end of the conductive plates 4a and 4b is folded to be substantially in the U-shaped form. The folded portions of the conductive plates 4a and 4b are connected to one end of the resistor 7. The adapter 5 is made of an insulating material and is used for fixing the key body 2 into the case 3. Namely, on assembling the key unit, the grip portion 2b is fitted in the adapter 5 as shown in FIG. 1(c) and then the adapter 5 with the key body 2 is fitted in the accommodating chamber of the case 3 as shown in FIG. 1(b). The contact piece 6 connects the grip portion 2b to the other end of the resistor 7.
When the key unit having the above construction is used, the user's fingers touch the contacting plates 4a and 4b. At this time, the static electricity charged on his body discharges along the route from the human body through the conductive plates 4a and 4b, the resistor 7 and the key body 2 to the lock of the earthed door. Accordingly, an electrical shock upon locking or unlocking can be prevented, if the resistance value of the resistor 7 is high enough.
With such a key unit, however, inconvenience is experienced during use or carriage, since the key unit is large sized.